Recently, in the automotive industry it is well known that for the purpose of reducing the body weight to achieve a reduction in fuel consumption, metal materials have been replaced by synthetic resin materials. Consequently, the amount of resin materials used per car has rapidly increased. The replacement of metal materials for synthetic resin materials, however, has been attempted mainly for interior parts of cars because synthetic resins are inferior to metal materials in various properties such as heat-resistance, weather-resistance and impact strength.
On the other hand, recently, synthetic resin materials, which are not electrically conductive in themselves, have been plated with metals due to advances in electroless plating technology. As a result, synthetic resin materials have been sharply improved in several properties such as weather-resistance, stiffness and hardness, which have been regarded as a disadvantages, and have been used in exterior parts of cars as a substitute for metal materials.
Synthetic resin materials have many advantages because they can be used to produce integral articles in one molding procedure, which have been assembled from many parts in the case of using metal materials, because they can be easily molded into complicated articles, and because they are light weight. These advantages are not attained in metal materials. As a result, synthetic resin materials can be very advantageously used because the body weight of cars can be reduced and a variety of designs can be achieved in addition to plating with metals using the electroless plating process.
Presently ABS resins have been most commonly used as a resin suitable for electroless plating. Many processes have been developed for plating ABS resins with metals, and a process which comprises oxidatively etching a polybutadiene component dispersed in the ABS resin using a mixed aqueous solution containing chromium trioxide and sulfuric acid to roughen the surface of the resin and introduce hydrophilic groups on the surface of the resin; activating the surface by depositing active species such as palladium; forming a thin coating layer of a metal such as copper and nickel thereon by an electroless plating process; and then forming a desired metal coating thereon by an electric plating process has employed.
ABS resins have been determined to be resins more suitable for plating due to close adhesion between the resin and the plated metal film, which results from selective etching of a polybutadiene component dispersed in the ABS resin resulting in the surface of the resin having minute concavo-convex holes in a homogeneous dispersed state, and an anchoring effect for the metal deposited in the convex holes. Accordingly, the adhesiveness of the metal film to the resin is affected by the content of the polybutadiene component in the ABS resin. On the contrary, while heat-resistance of the ABS resin tends to decrease proportionally to the increase in the content of the polybutadiene component in the resin, the heat distortion temperature of the ABS resin plated with metals, in general, has to be under 100.degree. C.
On the other hand, for example, in exterior parts of cars a resin having a heat distortion temperature higher than that of ABS resins, and in a hot-water supplying device parts, resins having a heat distortion temperature of 100.degree. C. and more are desired. Thus, the demand for resin materials suitable for electroless plating and having a higher heat distortion temperature has been increasing.